1. Field of the Invention
This invention relates to an improvement in a fluid coking process. More particularly it relates to recycling dry coke fines to the coking zone of the process. The term "fines" is intended herein to designate particles having a diameter size ranging up to about 74 microns.
2. Description of the Prior Art
It is known to produce fuel gases by integrated fluid coking and gasification processes such as those disclosed in U.S. Pat. Nos. 3,661,543; 3,702,516; and 3,759,676, the teachings of which are hereby incorporated by reference.
U.S. Pat. No. 3,414,504 discloses a fluid coking process in which a burner feul gas including entrained coke is combusted with air thereby producing heated dry coke particles which are recycled to the coker directly or in admixture with the oil feed.
U.S. Pat. No. 3,278,412 discloses a process for fluid coking in which coke-coated tar sands fines recovered from a low temperature burner are burned to remove the coke therefrom and the coke fines are subsequently recycled to a coking zone.
It is also known that a fluid coking process has been operated commercially with recycle of the dry coke fines removed from the coke burner to the coker by slurrying the dry fines with the coker oil feed prior to injecting the fines into the coker. Heretofore, it was assumed that if dry coke fines were recycled to the fluid coker, a large portion of the fines would escape overhead to the scrubber. The increased solids concentration in the slurry from the scrubber could then lead to plugging of the slurry circuit.
It has now been found that dry fines recovered from the gaseous effluent of a zone integrated with the coking zone can be advantageously recycled to the coking zone as dry fines without the necessity of mixing the fines with the coker oil feed, and without adversely affecting the process operation including the particle size distribution of the fluidized solids. Furthermore, in one embodiment of the invention wherein the process is an integrated coking and gasification process, the recycle fines permit a higher level of gasification of the gross coke product than heretofore. Recycling the fines also eliminates the coke fines disposal problem.